1. Field of the Invention
This invention pertains to the field of Head-Up Displays (singularly, “HUD”) that provide images in the field of view of a person viewing the scene outside of a vehicle such as an aircraft or automobile.
2. Description of the Related Art
A HUD is typically any transparent display that presents an image without obstructing the viewer's view or requiring the viewer to look away from the scene outside of a vehicle such as an aircraft or automobile while flying or driving. Initially developed for use in military aircraft, HUDs are used in commercial and private aircraft, automobiles, and other applications. HUD systems may be comprised of a plurality of components including, but not limited to, an image projection unit and a partially transparent and reflective optic commonly referred to as a combiner.
Generally, the field of view (“FOV”) of a HUD may be dependent on an Eye Reference Position (“ERP”). HUD performance characteristics such as required FOV may be measured from an ERP from where a HUD could be designed from optimal viewing. This position may serve as a reference point from which the viewer could enjoy optimal viewing. The size or fixed area of a HUD combiner unit on which the image is projected could determine a required FOV. A HUD combiner unit may be designed so that the image falls within the area of the combiner unit for the required FOV by a viewer from the ERP.
Since a combiner unit has a fixed area and the image display area may be conformal to the outside scene, images of symbology and terrain appear to expand when a viewer moves his or her eye position aft of the ERP and appear to contract when a viewer moves his or her eye position forward of the ERP. In effect, the movement of the viewer's eye position from the ERP changes the FOV available on the HUD combiner unit, but the image FOV projected on the combiner unit remains fixed and does not vary.